The present invention relates to an objective lens unit that is suitable as an optical pickup objective system, and further relates to the optical pickup device including this objective lens unit.
Until now, various kinds of optical pickup devices for reproducing and recording information on optical information recording media such as a CD (compact disc) or a DVD (digital video disc) and the like have been developed and manufactured and are being widely used. It is to be noted that “reproducing and recording” refers to reproduction and/or recording. Examples of the optical head device which is built into the optical pickup device include those in which the objective lens body and the phase control element are secured as a single unit inside a holder for stable recording and playing of both CDs and DVDs (Refer to Patent Document 1).
However, in the optical head device described above, because the structure is such that the two optical elements which are the objective lens and the phase control element are indirectly connected via the holder, alignment of both optical elements is not simple. In addition, there is a problem in that the degree of freedom for the configuration of the holder is limited by the size and distance between both optical elements because both optical elements are fixed in the holder.
Due to this problem, a method can be considered in which the two optical elements, which are the objective lens and the like, are provided with cylindrical flanges on their outer peripheries and both optical elements are directly joined together by the flange to form an optical lens unit which is a single part. In this case, the alignment accuracy of both optical elements can be ensured and assembly in holders with various shapes is simple.
However, for the above-described objective lens unit, there is a tendency for the girth of the objective lens unit to become large as a result of providing a flange of a thickness exceeding a predetermined amount on both optical elements which are the objective lens and the like, or because of securing space for adhering both optical elements to each other.
In the optical pickup device including the above-described objective lens unit, securing the objective lens unit to the front end side of the cylindrical holder may be considered in order to lighten the movable portion of the objective system including the objective lens unit. However in this case, the diameter of the holder is increased to correspond with the increased diameter of the objective lens unit and the weight of the movable portion of the objective system is increased and there is a tendency for the responsiveness of the movable portion to deteriorate. On the other hand, if the diameter of optical elements such as the objective lens and the phase control element, and thus that of the objective lens unit, is not larger than a certain amount, the information cannot be reproduced and recorded using NA conforming to the standard. In particular, in recent times, there has been a strong desire for objective lenses which meet the high NA standards and the diameter of the optical elements such as the objective lenses and phase control elements and the like must be above a certain value.
[Patent Document 1] Unexamined Japanese Patent Application Publication No. 2001-6203